This invention relates to copy or recording machines as used in the fields of facsimile, electronic computer terminals, various kinds of control systems, and medical equipments, and, in particular, to fiber-optic, or optical fiber, cathode ray tubes used in such copy machines.
A known copy machine comprises, as schematically shown in FIG. 1, a flying spot tube 1, an optical system including a spherical lens 3 and a photosensitive medium 4. The image 2 displayed on the face plate of the flying spot tube 1 is recorded on the photosensitive medium 4 through the optical system to provide a hard copy.
But this system has disadvantages that the brightness of the image is remarkably reduced by the use of the optical system, that a high-resolution of the flying spot tube is required for a clear record, that a lengthy optical path is required to the optical system and that the optical system is weak to mechanical vibration.
Another known copy machine is one using an optical fiber cathode ray tube (CRT).
The optical fiber CRT 6 is, as shown in FIGS. 2(a)-2(c), a type of cathode ray tube having an electron gun 61 and a face plate 62. The optical fiber CRT 6 is characterized in that the face plate 62 is a stack of glass fibers. The stack consists of a large number of parallel glass fibers of small diameter each of which is sheathed with a glass having a lower refractive index than that of the fiber glass. The fiber ends from the inner and the outer surfaces of the face plate. The phosphor is deposited on the inner surface of the face plate.
Referring to FIG. 3 in which the construction of the optical fiber CRT is schematically shown, an electron beam 7 is emitted from the electron gun 61 and the phosphor 8 is thereby bombarded and excited to illuminate. The luminous light is emitted from the fibers 9 of the optical fiber face plate 62. The spreading of the emitted light beam 10 depends on the distance from the face plate and the numerical aperture of the face plate.
At the outer surface of the face plate 61, an increased brightness of about 100 times in comparison with the use of the optical system as shown in FIG. 1 and a high resolution are obtained, but they become reduced at a distance from the outer surface of the face plate.
Accordingly, in the known copy machine using an optical fiber CRT, the photosensitive medium 11 must be disposed not apart from the face plate 62 as shown in FIG. 3 but also in direct contact with the face plate as shown in FIG. 4.
Referring to FIG. 4, an electrographic paper 12 as a photosensitive medium is pressed onto the face plate 62 of the optical fiber CRT 6 by a pressure roll 13.
On the other hand, not only electrographic papers such as electrofaxes and dry graphic papers such as dry silver photographic papers but also CdS coated drums and Se (selenium) coated drums are used as a photosensitive medium. In copy machines using plain paper, a CdS or Se coated drum is used for a photosensitive medium. The CdS coating and the Se coating are very weak and are readily injured by friction and mechanical engagement with an object.
Therefore, the optical fiber CRT has not been used in copy machines using a CdS or Se coated drum as a photosensitive medium.